Water may contain many different kinds of contaminants including, for example, particulates, harmful chemicals, and microbiological organisms, such as bacteria, parasites, protozoa and viruses. In a variety of circumstances, these contaminants must be removed before the water can be used. For example, in many medical applications and in the manufacture of certain electronic components, extremely pure water is required. As a more common example, any harmful contaminants must be removed from the water before it is potable, i.e., fit to consume. Despite modern water purification means, the general population is at risk, and in particular infants and persons with compromised immune systems are at considerable risk.
In the U.S. and other developed countries, municipally treated water typically includes one or more of the following impurities to various levels: suspended solids, chemical contaminants, such as organic matter, and heavy metals, and microbiological contaminants, such as bacteria, parasites, and viruses. Breakdown and other problems with water treatment systems sometimes lead to incomplete removal of these contaminants. In other countries, there are deadly consequences associated with exposure to contaminated water, as some of them have increasing population densities, increasingly scarce water resources, and no water treatment utilities. It is common for sources of drinking water to be in close proximity to human and animal waste, such that microbiological contamination is a major health concern. As a result of waterborne microbiological contamination, an estimated six million people die each year, half of which are children under 5 years of age.
The reduction of the general contaminant concentration in the potable water takes place at the municipal treatment facilities and in homes with point-of-entry (POE) and/or point-of-use (POU) water filters. This reduction in concentration in the home water filters is achieved by mechanical filtration, (i.e., size exclusion for some particulates, parasites, and bacteria), and adsorption (i.e., chemicals, some particulates, parasites, bacteria, and viruses). For home water filters, the concentration reduction levels depend on the flowrate, filter volume and shape, influent concentration levels, and capture kinetics and capacity of the filtration medium. For the purposes of this invention, the capture kinetics and capacity of the medium is encompassed in the term “capture efficiency”. Furthermore, if the concentration reduction levels achieved by home water filters reach the levels mandated by various domestic or international organizations (e.g., U.S. Environmental Protection Agency—EPA, National Sanitation Foundation—NSF, and World Health Organization—WHO) in pertinent testing standards and protocols, then the water filters can be registered by these organizations and carry the applicable registration numbers. Similar tests and standards apply to air filters.
For example, the EPA introduced the “Guide Standard and Protocol for Testing Microbiological Water Purifiers” in 1987. This protocol establishes minimum requirements regarding the performance of drinking water treatment systems that are designed to reduce specific health related contaminants in public or private water supplies. The requirements are that the effluent from a water supply source exhibits 99.99% (or equivalently, 4 log) removal of viruses and 99.9999% (or equivalently, 6 log) removal of bacteria against a challenge. Under the EPA protocol, in the case of viruses, the influent concentration should be 1×107 viruses per liter, and in the case of bacteria, the influent concentration should be 1×108 bacteria per liter. Because of the prevalence of Escherichia coli (E. coli, bacterium) in water supplies, and the risks associated with its consumption, this microorganism is used as the bacterium in the majority of studies. Similarly, the MS-2 bacteriophage (or simply, MS-2 phage) is typically used as the representative microorganism for virus removal because its size and shape (i.e., about 26 nm and icosahedral) are similar to many viruses. Thus, a filter's ability to remove MS-2 bacteriophage demonstrates its ability to remove other viruses.
Similar protocols and/or standards exist for chemical and particulate concentration reductions established by NSF. For example, NSF/ANSI Standard 42 covers the aesthetic effects of POU and POE systems designed to reduce specific aesthetic or non-health-related contaminants, such as chlorine, taste and odor, and particulates. Similarly, NSF/ANSI Standard 53 covers the health effects of POU and POE systems designed to reduce specific health-related contaminants, such as Cryptosporidium, Giardia, lead, volatile organic chemicals (VOCs), and methyl tertiary-butyl ether (MTBE).
Due to these requirements and a general interest in improving the quality of potable water, there is a continuing desire to provide improved filters and filter materials capable of removing contaminants from a water stream, as well as a desire to provide improved methods of making and using the filter materials, and filters incorporating the filter materials.